Letters sent home by Kenneth Bae, an American citizen imprisoned in North Korea for alleged crimes against the state, show a "new note of desperation", his sister said, as the US seeks to prevent the Christian missionary from becoming a high-profile diplomatic bargaining chip.
Bae was sentenced in early May to 15 years of hard labour after North Korean authorities convicted him of what it said was an attempt at state subversion. Authorities there said the 44-year-old used his tourism business to form groups to overthrow the government.
Bae has been held since November, and his sentencing came amid acrimonious relations between Pyongyang and Washington over the reclusive state's nuclear aspirations.
"He is asking us directly and saying, 'My health is failing, I need help.' There is a new note of desperation," Bae's sister, Terri Chung, told Seattle NBC affiliate King5 in an interview aired on Thursday.
Chung said she had received handwritten letters postmarked from Pyongyang in June from Bae, who suffers from diabetes, which may be causing blindness.
Bae, looking thinner, appeared in an edited interview aired on CNN in early July wearing a dirty, blue-grey prison uniform, in which he asked US officials for help securing his freedom and asked North Korean officials for forgiveness.
"Please don't lose hope," Chung said she has written in e-mail exchanges brokered by the US State Department.
Bae is a naturalised US citizen who was born in South Korea. He most recently lived in China.
North Korea has in the past used the release of high-profile American prisoners as a means of garnering a form of prestige or acceptance, rather than economic gain, portraying visiting dignitaries as paying homage to the country and its leader.
That pattern has complicated the response from US lawmakers and the State Department, which has called for Bae's immediate release on "humanitarian grounds" but resisted sending high-profile envoys to negotiate, as it has done in the past.
"The more public action, the more government attention there is raises the value as a prisoner for Bae," said a Congressional aide familiar with such diplomatic efforts, who declined to be named.
An internet petition urging US President Barack Obama to secure "special amnesty" for Bae has garnered roughly 4,000 signatures. Meanwhile, Bae's family plans a prayer vigil in Seattle on August 6.